1. Field of Invention
This invention relates generally to a system which monitors data generated by an electric utility meter representing electrical power demand and is effective to generate commands to temporarily shut off predetermined electrical loads during peak demand periods. This invention provides a programmable means of limiting peak demand along with biofeedback indicators displaying the demand state directly to the electric power consumer.
2. Description of Prior Art
For energy conservation and potential reduction in consumer utility bills, many techniques have been proposed for automatically limiting peak demands for electrical power. Power demand exceeding the baseline generating capacity of a typical electric utility company requires utilization of inefficient peaking generators. Power demand falling below baseline capacity results in inefficient usage of generated power. Load control techniques provide a potential solution, smoothing the power demand curve to more efficiently match baseline generating capacity.
Well-known technology presently exists affording control of desired loads for peak demand smoothing and some techniques have been implemented primarily for industrial customers. However, the prior art has yet to solve efficiently the problems of reliable demand monitoring and control cable installation in a manner acceptable to residential customers. Prior art systems include two general categories: centralized control systems, such as disclosed in U.S. Pat. No. 3,909,821 and decentralized or local control systems, as disclosed in U.S. Pat. No. 4,147,978. Central control systems monitor total demand at the generating facility. When a peak demand is anticipated, load control commands are generated and communicated to individually metered loads in order to deactivate all the predetermined loads (e.g., hot water heaters), in a general area. Although such an approach has technical merit, the primary disadvantage resides in a lack of consumer acceptance and high unit cost. The high cost of centralized systems affected by the cost of communicating load control commands to individual loads has precluded a large scale implementation.
Local control systems must monitor power demand at the actual point of use, generate load commands when local demand peaks are detected, communicate the commands to the specific point of control and deactivate the desired load. Prior art systems typically monitor demand at the electric meter with a loop current probe which generates an analog signal proportional to the electric current flow. When the analog value reaches a predetermined threshold indicating a peak demand, load control command is generated and communicated to the control point either at the circuit breaker box or at the load by means of communication control cables. Although such systems are significantly more economical than centralized systems, local load control systems suffer from the disadvantage of poor accuracy inherent in low cost analog systems and high installation cost required for extending communication control cables to the point of control. In the case of some residential applications, installing cables through existing structures is not only cost prohibitive, but precludes consumer acceptance. Although automatic load control shows the potential for a vast contribution toward energy conservation, no single technique has been accepted for application on a large scale.